Frequency-hopping spread spectrum (FHSS) communications systems operate by subdividing the available bandwidth into a large number of channels, each having different frequencies. In any signaling interval, the transmitted signal occupies one or more of the available channels. The selection of channels in each signaling interval is made by a pseudorandom function. Frequency-hopped spread spectrum systems are generally classified as either fast frequency-hopping systems, or slow frequency-hopping systems depending upon how often the carrier frequency is changed relative to the symbol interval.
Transmitters in typical FHSS systems are not synchronized with each other. As such there is a chance of mutual interference among transmitters. This mutual interference includes adjacent channel collisions and co-channel collisions. FIG. 1 is a prior art FHSS channel hopping sequence chart showing adjacent and co-channel collisions. The probability of mutual interference is proportional to the number of independent FHSS systems in an area.
When the number of independent FHSS systems in an area is small there is a small chance of mutual interference. This is because a small number of FHSS systems in an area, each using an independent algorithm to generate symbol timing and frequency hop sequence, have a low probability of collision.
When the number of independent FHSS systems operating in an area or region grows, the probability of mutual interference increases because a larger number of systems are competing for the same number of communication channels. Throughput loss is experienced due to channel collisions 102 when two or more transmitters (N) hop to the same frequency, or adjacent channel collisions 104 when two or more transmitters hop to adjacent frequencies. Any receiving systems that happen to be in range of two or more of the N transmitters will experience interference during the time when the transmitters are transmitting. Any data transmitted during that interference time is lost. Recovery methods may be used, but the throughput, or available bandwidth for communications, is reduced in direct proportion to the rate of these channel collisions.
In environments where large numbers of FHSS wireless systems are operating, mutual interference between systems decreases the throughput performance of all systems. Typical methods used to reduce the interference effect of multiple systems transmitting on the same frequency include synchronizing the symbol timing of the systems, and using different hop sequences in each FHSS system. However, these techniques require specific systems, or a network of systems, to track and control transmission frequency calculations for all of the FHSS wireless systems in the area.
To increase throughput performance in systems using Bluetooth™, the use of high performance radios has been recommended to mitigate packet loss in areas with high amounts of interference. This only addresses the adjacent channel interference and does not help co-channel interference. Consequently, the overall effect on throughput is minimal. Further, the use of high performance radios can significantly increase the cost of the Bluetooth™ equipment, thereby making the equipment unaffordable to the targeted consumer.
In the drawings, the same reference numbers identify identical or substantially similar elements or acts. To easily identify the discussion of any particular element or act, the most significant digit or digits in a reference number refer to the Figure number in which that element is first introduced (e.g., element 404 is first introduced and discussed with respect to FIG. 4).
The headings provided herein are for convenience only, and do not necessarily affect the scope or meaning of the claimed invention.